sc_neurocore_engine/neurons/

maps.rs

// SPDX-License-Identifier: AGPL-3.0-or-later
// Commercial license available
// © Concepts 1996–2026 Miroslav Šotek. All rights reserved.
// © Code 2020–2026 Miroslav Šotek. All rights reserved.
// ORCID: 0009-0009-3560-0851
// Contact: www.anulum.li | protoscience@anulum.li
// SC-NeuroCore — Discrete map neuron models

//! Discrete map neuron models.

/// Chialvo 1995 — 2D discrete map neuron.
#[derive(Clone, Debug)]
pub struct ChialvoMapNeuron {
    pub x: f64,
    pub y: f64,
    pub a: f64,
    pub b: f64,
    pub c: f64,
    pub k: f64,
    pub x_threshold: f64,
}

impl ChialvoMapNeuron {
    pub fn new() -> Self {
        Self {
            x: 0.0,
            y: 0.0,
            a: 0.89,
            b: 0.6,
            c: 0.28,
            k: 0.04,
            x_threshold: 1.0,
        }
    }
    pub fn step(&mut self, current: f64) -> i32 {
        let x_prev = self.x;
        let x_new = self.x * self.x * (self.y - self.x).exp() + self.k + current;
        let y_new = self.a * self.y - self.b * self.x + self.c;
        self.x = x_new;
        self.y = y_new;
        if self.x >= self.x_threshold && x_prev < self.x_threshold {
            1
        } else {
            0
        }
    }
    pub fn reset(&mut self) {
        self.x = 0.0;
        self.y = 0.0;
    }
}
impl Default for ChialvoMapNeuron {
    fn default() -> Self {
        Self::new()
    }
}

/// Rulkov 2001 — piecewise nonlinear map for fast/slow bursting.
#[derive(Clone, Debug)]
pub struct RulkovMapNeuron {
    pub x: f64,
    pub y: f64,
    pub alpha: f64,
    pub sigma: f64,
    pub mu: f64,
    pub x_threshold: f64,
}

impl RulkovMapNeuron {
    pub fn new() -> Self {
        Self {
            x: -1.0,
            y: -3.0,
            alpha: 4.0,
            sigma: -1.6,
            mu: 0.001,
            x_threshold: 0.0,
        }
    }
    pub fn step(&mut self, current: f64) -> i32 {
        let x_prev = self.x;
        let x_new = if self.x <= 0.0 {
            self.alpha / (1.0 - self.x) + self.y + current
        } else if self.x < self.alpha + self.y + current {
            self.alpha + self.y + current
        } else {
            -1.0
        };
        let y_new = self.y - self.mu * (self.x + 1.0) + self.mu * self.sigma;
        self.x = x_new;
        self.y = y_new;
        if self.x >= self.x_threshold && x_prev < self.x_threshold {
            1
        } else {
            0
        }
    }
    pub fn reset(&mut self) {
        self.x = -1.0;
        self.y = -3.0;
    }
}
impl Default for RulkovMapNeuron {
    fn default() -> Self {
        Self::new()
    }
}

/// Ibarz-Tanaka map — piecewise-linear spiking map.
#[derive(Clone, Debug)]
pub struct IbarzTanakaMapNeuron {
    pub x: f64,
    pub y: f64,
    pub alpha: f64,
    pub beta: f64,
    pub mu: f64,
    pub sigma: f64,
    pub x_threshold: f64,
    pub x_reset: f64,
}

impl IbarzTanakaMapNeuron {
    pub fn new() -> Self {
        Self {
            x: -1.0,
            y: -2.5,
            alpha: 3.65,
            beta: 0.25,
            mu: 0.0005,
            sigma: -1.6,
            x_threshold: 3.0,
            x_reset: -1.0,
        }
    }
    pub fn step(&mut self, current: f64) -> i32 {
        let f = if self.x <= 0.0 {
            self.alpha / (1.0 - self.x)
        } else {
            self.alpha + self.beta * self.x
        };
        let x_new = f + self.y + current;
        let y_new = self.y - self.mu * (self.x + 1.0) + self.mu * self.sigma;
        self.x = x_new;
        self.y = y_new;
        if self.x >= self.x_threshold {
            self.x = self.x_reset;
            1
        } else {
            0
        }
    }
    pub fn reset(&mut self) {
        self.x = -1.0;
        self.y = -2.5;
    }
}
impl Default for IbarzTanakaMapNeuron {
    fn default() -> Self {
        Self::new()
    }
}

/// Medvedev map — piecewise monotone 1D neuron map.
#[derive(Clone, Debug)]
pub struct MedvedevMapNeuron {
    pub x: f64,
    pub alpha: f64,
    pub beta: f64,
    pub x_threshold: f64,
}

impl MedvedevMapNeuron {
    pub fn new() -> Self {
        Self {
            x: 0.0,
            alpha: 3.5,
            beta: 0.5,
            x_threshold: 0.9,
        }
    }
    pub fn step(&mut self, current: f64) -> i32 {
        let x_prev = self.x;
        self.x = if self.x < self.beta {
            self.alpha * self.x + current
        } else {
            self.alpha * (1.0 - self.x) + current
        };
        self.x = self.x.rem_euclid(1.0);
        if self.x >= self.x_threshold && x_prev < self.x_threshold {
            1
        } else {
            0
        }
    }
    pub fn reset(&mut self) {
        self.x = 0.0;
    }
}
impl Default for MedvedevMapNeuron {
    fn default() -> Self {
        Self::new()
    }
}

/// Cazelles logistic map neuron — coupled 2D logistic with slow variable.
#[derive(Clone, Debug)]
pub struct CazellesMapNeuron {
    pub x: f64,
    pub y: f64,
    pub a: f64,
    pub epsilon: f64,
    pub sigma: f64,
    pub x_threshold: f64,
}

impl CazellesMapNeuron {
    pub fn new() -> Self {
        Self {
            x: 0.1,
            y: 0.0,
            a: 3.8,
            epsilon: 0.01,
            sigma: 0.5,
            x_threshold: 0.9,
        }
    }
    pub fn step(&mut self, current: f64) -> i32 {
        let f = self.a * self.x * (1.0 - self.x);
        let x_new = (f - self.y + current).clamp(-2.0, 2.0);
        let y_new = self.y + self.epsilon * (self.x - self.sigma);
        self.x = x_new;
        self.y = y_new;
        if self.x >= self.x_threshold {
            1
        } else {
            0
        }
    }
    pub fn reset(&mut self) {
        self.x = 0.1;
        self.y = 0.0;
    }
}
impl Default for CazellesMapNeuron {
    fn default() -> Self {
        Self::new()
    }
}

/// Courbage-Nekorkin piecewise-linear Lorenz-type map.
#[derive(Clone, Debug)]
pub struct CourageNekorkinMapNeuron {
    pub x: f64,
    pub y: f64,
    pub alpha: f64,
    pub beta: f64,
    pub j: f64,
    pub x_threshold: f64,
}

impl CourageNekorkinMapNeuron {
    pub fn new() -> Self {
        Self {
            x: 0.0,
            y: 0.0,
            alpha: 3.0,
            beta: 0.001,
            j: 0.1,
            x_threshold: 1.0,
        }
    }
    pub fn step(&mut self, current: f64) -> i32 {
        let x_prev = self.x;
        let f = if self.x < 0.0 {
            self.alpha * self.x
        } else {
            self.alpha * self.x / (1.0 + self.alpha * self.x)
        };
        let x_new = (f + self.y + current + self.j).clamp(-1e6, 1e6);
        let y_new = (self.y - self.beta * (self.x + 1.0)).clamp(-1e6, 1e6);
        self.x = if x_new.is_finite() { x_new } else { 0.0 };
        self.y = if y_new.is_finite() { y_new } else { 0.0 };
        if self.x >= self.x_threshold && x_prev < self.x_threshold {
            1
        } else {
            0
        }
    }
    pub fn reset(&mut self) {
        self.x = 0.0;
        self.y = 0.0;
    }
}
impl Default for CourageNekorkinMapNeuron {
    fn default() -> Self {
        Self::new()
    }
}

/// Aihara 1990 — chaotic neuron map with sigmoid nonlinearity.
///
/// 2D discrete map producing chaotic spiking, bursting, and tonic firing
/// depending on parameters. The sigmoid output function models the
/// nonlinear voltage-to-firing-rate relationship.
///
/// x(n+1) = k_f * x(n) / (1 + exp(-(x(n) + alpha))) - y(n) + I
/// y(n+1) = k_s * y(n) + delta * x(n)
///
/// Aihara et al., Phys Lett A 144:333, 1990.
#[derive(Clone, Debug)]
pub struct AiharaMapNeuron {
    pub x: f64,
    pub y: f64,
    pub k_f: f64,   // Fast variable decay
    pub k_s: f64,   // Slow variable decay
    pub alpha: f64, // Sigmoid steepness offset
    pub delta: f64, // Slow→fast coupling
    pub x_threshold: f64,
}

impl Default for AiharaMapNeuron {
    fn default() -> Self {
        Self::new()
    }
}

impl AiharaMapNeuron {
    pub fn new() -> Self {
        Self {
            x: 0.0,
            y: 0.0,
            k_f: 0.7,
            k_s: 0.95,
            alpha: 2.0,
            delta: 0.05,
            x_threshold: 0.5,
        }
    }

    pub fn step(&mut self, current: f64) -> i32 {
        let x_prev = self.x;
        let sigmoid = 1.0 / (1.0 + (-(self.x + self.alpha)).exp());
        let x_new = self.k_f * self.x * sigmoid - self.y + current;
        let y_new = self.k_s * self.y + self.delta * self.x;

        self.x = x_new.clamp(-10.0, 10.0);
        self.y = y_new.clamp(-10.0, 10.0);

        if !self.x.is_finite() {
            self.x = 0.0;
        }
        if !self.y.is_finite() {
            self.y = 0.0;
        }

        if self.x >= self.x_threshold && x_prev < self.x_threshold {
            1
        } else {
            0
        }
    }

    pub fn reset(&mut self) {
        *self = Self::new();
    }
}

/// Kilinc-Bhatt 2023 — sigmoid map with adaptive threshold.
///
/// Minimal 2D map with built-in spike frequency adaptation via
/// a slow threshold variable. Designed for efficient hardware
/// implementation while retaining biologically relevant dynamics.
///
/// x(n+1) = k * sigmoid(x(n) - theta(n)) + I
/// theta(n+1) = beta * theta(n) + gamma * H(x(n) - theta_spike)
///
/// H() is the Heaviside step function (spike-triggered increment).
#[derive(Clone, Debug)]
pub struct KilincBhattMapNeuron {
    pub x: f64,
    pub theta: f64,       // Adaptive threshold
    pub k: f64,           // Gain
    pub beta: f64,        // Threshold decay
    pub gamma: f64,       // Spike→threshold coupling
    pub theta_spike: f64, // Spike detection level
    pub x_threshold: f64,
}

impl Default for KilincBhattMapNeuron {
    fn default() -> Self {
        Self::new()
    }
}

impl KilincBhattMapNeuron {
    pub fn new() -> Self {
        Self {
            x: 0.0,
            theta: 0.0,
            k: 1.5,
            beta: 0.95,
            gamma: 0.3,
            theta_spike: 0.8,
            x_threshold: 0.8,
        }
    }

    pub fn step(&mut self, current: f64) -> i32 {
        let x_prev = self.x;
        let sig = 1.0 / (1.0 + (-(self.x - self.theta) * 4.0).exp());
        let x_new = -self.x + self.k * sig + current;
        let spiked = if self.x >= self.theta_spike { 1.0 } else { 0.0 };
        let theta_new = self.beta * self.theta + self.gamma * spiked;

        self.x = x_new.clamp(-5.0, 5.0);
        self.theta = theta_new.clamp(-5.0, 5.0);

        if !self.x.is_finite() {
            self.x = 0.0;
        }
        if !self.theta.is_finite() {
            self.theta = 0.0;
        }

        if self.x >= self.x_threshold && x_prev < self.x_threshold {
            1
        } else {
            0
        }
    }

    pub fn reset(&mut self) {
        *self = Self::new();
    }
}

/// Ermentrout-Kopell canonical Type I — theta neuron in map form.
///
/// The canonical model for Type I (saddle-node) excitability.
/// theta(n+1) = theta(n) + dt * (1 - cos(theta)) + (1 + cos(theta)) * I
/// Spike when theta crosses pi.
///
/// Ermentrout & Kopell, SIAM J Appl Math 46:233, 1986.
#[derive(Clone, Debug)]
pub struct ErmentroutKopellMapNeuron {
    pub theta: f64, // Phase variable [0, 2*pi)
    pub dt: f64,
    pub gain: f64,
    pub theta_threshold: f64,
}

impl Default for ErmentroutKopellMapNeuron {
    fn default() -> Self {
        Self::new()
    }
}

impl ErmentroutKopellMapNeuron {
    pub fn new() -> Self {
        Self {
            theta: 0.0,
            dt: 0.1, // Discrete step size
            gain: 1.0,
            theta_threshold: std::f64::consts::PI,
        }
    }

    pub fn step(&mut self, current: f64) -> i32 {
        let input = self.gain * current;
        let theta_prev = self.theta;

        let d_theta = (1.0 - self.theta.cos()) + (1.0 + self.theta.cos()) * input;
        self.theta += self.dt * d_theta;

        // Spike detection: crossing pi
        let fired = if self.theta >= self.theta_threshold && theta_prev < self.theta_threshold {
            1
        } else {
            0
        };

        // Wrap theta to [0, 2*pi)
        let two_pi = 2.0 * std::f64::consts::PI;
        if self.theta >= two_pi {
            self.theta -= two_pi;
        }
        if self.theta < 0.0 {
            self.theta += two_pi;
        }

        if !self.theta.is_finite() {
            self.theta = 0.0;
        }

        fired
    }

    pub fn reset(&mut self) {
        *self = Self::new();
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn chialvo_fires() {
        let mut n = ChialvoMapNeuron::new();
        let t: i32 = (0..1000).map(|_| n.step(1.0)).sum();
        assert!(t > 0);
    }
    #[test]
    fn rulkov_fires() {
        let mut n = RulkovMapNeuron::new();
        let t: i32 = (0..2000).map(|_| n.step(0.5)).sum();
        assert!(t > 0);
    }
    #[test]
    fn ibarz_fires() {
        let mut n = IbarzTanakaMapNeuron::new();
        let t: i32 = (0..2000).map(|_| n.step(2.0)).sum();
        assert!(t > 0);
    }
    #[test]
    fn medvedev_fires() {
        let mut n = MedvedevMapNeuron {
            x: 0.5,
            ..Default::default()
        };
        let t: i32 = (0..500).map(|_| n.step(0.1)).sum();
        assert!(t > 0);
    }
    #[test]
    fn cazelles_fires() {
        let mut n = CazellesMapNeuron::new();
        let t: i32 = (0..200).map(|_| n.step(0.0)).sum();
        assert!(t > 0);
    }
    #[test]
    fn cournekorkin_fires() {
        let mut n = CourageNekorkinMapNeuron::new();
        let t: i32 = (0..200).map(|_| n.step(0.5)).sum();
        assert!(t > 0);
    }

    // -- Aihara Map coverage tests --

    #[test]
    fn aihara_fires_with_input() {
        let mut n = AiharaMapNeuron::new();
        let t: i32 = (0..2000).map(|_| n.step(1.0)).sum();
        assert!(t > 0, "Aihara must fire with input, got {t}");
    }

    #[test]
    fn aihara_silent_without_input() {
        let mut n = AiharaMapNeuron::new();
        let t: i32 = (0..5000).map(|_| n.step(0.0)).sum();
        assert_eq!(t, 0, "Aihara must be silent without input, got {t}");
    }

    #[test]
    fn aihara_chaotic_dynamics() {
        // With appropriate input, trajectory should not settle to fixed point
        let mut n = AiharaMapNeuron::new();
        let mut values = Vec::new();
        for _ in 0..1000 {
            n.step(0.5);
            values.push(n.x);
        }
        let mean = values.iter().sum::<f64>() / values.len() as f64;
        let var = values.iter().map(|v| (v - mean).powi(2)).sum::<f64>() / values.len() as f64;
        assert!(
            var > 0.001,
            "Trajectory should show variability (chaos), var={var}"
        );
    }

    #[test]
    fn aihara_negative_input_no_crash() {
        let mut n = AiharaMapNeuron::new();
        for _ in 0..10_000 {
            n.step(-100.0);
        }
        assert!(n.x.is_finite());
    }

    #[test]
    fn aihara_nan_input_stays_finite() {
        let mut n = AiharaMapNeuron::new();
        n.step(f64::NAN);
        assert!(n.x.is_finite());
    }

    #[test]
    fn aihara_extreme_input_bounded() {
        let mut n = AiharaMapNeuron::new();
        for _ in 0..1000 {
            n.step(1e6);
        }
        assert!(n.x.is_finite() && n.x <= 1e6);
    }

    #[test]
    fn aihara_reset_clears_state() {
        let mut n = AiharaMapNeuron::new();
        for _ in 0..100 {
            n.step(1.0);
        }
        n.reset();
        assert_eq!(n.x, 0.0);
        assert_eq!(n.y, 0.0);
    }

    #[test]
    fn aihara_rate_increases_with_input() {
        let mut low = AiharaMapNeuron::new();
        let mut high = AiharaMapNeuron::new();
        let spikes_low: i32 = (0..5000).map(|_| low.step(0.5)).sum();
        let spikes_high: i32 = (0..5000).map(|_| high.step(2.0)).sum();
        assert!(
            spikes_high >= spikes_low,
            "Higher input should produce more spikes: high={spikes_high} vs low={spikes_low}"
        );
    }

    #[test]
    fn aihara_performance_100k_steps() {
        let start = std::time::Instant::now();
        let mut n = AiharaMapNeuron::new();
        for _ in 0..100_000 {
            std::hint::black_box(n.step(0.5));
        }
        let elapsed = start.elapsed();
        assert!(
            elapsed.as_millis() < 50,
            "100k steps must complete in <50ms"
        );
    }

    // -- Kilinc-Bhatt Map coverage tests --

    #[test]
    fn kb_fires_with_input() {
        let mut n = KilincBhattMapNeuron::new();
        let t: i32 = (0..5000).map(|_| n.step(1.0)).sum();
        assert!(t > 0, "KB must fire with input, got {t}");
    }

    #[test]
    fn kb_silent_without_input() {
        let mut n = KilincBhattMapNeuron::new();
        let t: i32 = (0..5000).map(|_| n.step(0.0)).sum();
        assert_eq!(t, 0, "KB must be silent without input, got {t}");
    }

    #[test]
    fn kb_adaptation() {
        // Theta increases with spiking → fewer spikes over time
        let mut n = KilincBhattMapNeuron::new();
        let early: i32 = (0..2000).map(|_| n.step(1.0)).sum();
        let late: i32 = (0..2000).map(|_| n.step(1.0)).sum();
        assert!(
            early >= late,
            "Adaptation should slow firing: early={early}, late={late}"
        );
    }

    #[test]
    fn kb_theta_increases_during_spiking() {
        let mut n = KilincBhattMapNeuron::new();
        let theta_before = n.theta;
        for _ in 0..5000 {
            n.step(1.5);
        }
        assert!(
            n.theta > theta_before,
            "Theta must increase during spiking, theta={}",
            n.theta
        );
    }

    #[test]
    fn kb_negative_input_no_crash() {
        let mut n = KilincBhattMapNeuron::new();
        for _ in 0..10_000 {
            n.step(-100.0);
        }
        assert!(n.x.is_finite());
    }

    #[test]
    fn kb_nan_input_stays_finite() {
        let mut n = KilincBhattMapNeuron::new();
        n.step(f64::NAN);
        assert!(n.x.is_finite());
    }

    #[test]
    fn kb_extreme_input_bounded() {
        let mut n = KilincBhattMapNeuron::new();
        for _ in 0..1000 {
            n.step(1e6);
        }
        assert!(n.x.is_finite() && n.x <= 5.0);
    }

    #[test]
    fn kb_reset_clears_state() {
        let mut n = KilincBhattMapNeuron::new();
        for _ in 0..100 {
            n.step(1.0);
        }
        n.reset();
        assert_eq!(n.x, 0.0);
        assert_eq!(n.theta, 0.0);
    }

    #[test]
    fn kb_performance_100k_steps() {
        let start = std::time::Instant::now();
        let mut n = KilincBhattMapNeuron::new();
        for _ in 0..100_000 {
            std::hint::black_box(n.step(0.5));
        }
        let elapsed = start.elapsed();
        assert!(
            elapsed.as_millis() < 50,
            "100k steps must complete in <50ms"
        );
    }

    // -- Ermentrout-Kopell Map coverage tests --

    #[test]
    fn ek_fires_with_input() {
        let mut n = ErmentroutKopellMapNeuron::new();
        let t: i32 = (0..5000).map(|_| n.step(0.5)).sum();
        assert!(t > 0, "EK must fire with input, got {t}");
    }

    #[test]
    fn ek_silent_without_input() {
        // Type I: no firing below threshold (I < 0 is subthreshold for theta model)
        let mut n = ErmentroutKopellMapNeuron::new();
        let t: i32 = (0..5000).map(|_| n.step(-0.1)).sum();
        assert_eq!(t, 0, "EK must be silent with negative input, got {t}");
    }

    #[test]
    fn ek_type_i_excitability() {
        // Type I: arbitrarily low firing rate near threshold
        let mut n_low = ErmentroutKopellMapNeuron::new();
        let mut n_high = ErmentroutKopellMapNeuron::new();
        let spikes_low: i32 = (0..10_000).map(|_| n_low.step(0.01)).sum();
        let spikes_high: i32 = (0..10_000).map(|_| n_high.step(1.0)).sum();
        assert!(
            spikes_high > spikes_low,
            "Higher input → higher rate: high={spikes_high} vs low={spikes_low}"
        );
    }

    #[test]
    fn ek_theta_wraps() {
        // Theta should stay in [0, 2*pi)
        let mut n = ErmentroutKopellMapNeuron::new();
        for _ in 0..10_000 {
            n.step(0.5);
        }
        let two_pi = 2.0 * std::f64::consts::PI;
        assert!(
            n.theta >= 0.0 && n.theta < two_pi,
            "Theta must wrap to [0, 2pi), theta={}",
            n.theta
        );
    }

    #[test]
    fn ek_negative_input_no_crash() {
        let mut n = ErmentroutKopellMapNeuron::new();
        for _ in 0..10_000 {
            n.step(-100.0);
        }
        assert!(n.theta.is_finite());
    }

    #[test]
    fn ek_nan_input_stays_finite() {
        let mut n = ErmentroutKopellMapNeuron::new();
        n.step(f64::NAN);
        assert!(n.theta.is_finite());
    }

    #[test]
    fn ek_extreme_input_bounded() {
        let mut n = ErmentroutKopellMapNeuron::new();
        for _ in 0..1000 {
            n.step(1e6);
        }
        assert!(n.theta.is_finite());
    }

    #[test]
    fn ek_reset_clears_state() {
        let mut n = ErmentroutKopellMapNeuron::new();
        for _ in 0..100 {
            n.step(0.5);
        }
        n.reset();
        assert_eq!(n.theta, 0.0);
    }

    #[test]
    fn ek_performance_100k_steps() {
        let start = std::time::Instant::now();
        let mut n = ErmentroutKopellMapNeuron::new();
        for _ in 0..100_000 {
            std::hint::black_box(n.step(0.5));
        }
        let elapsed = start.elapsed();
        assert!(
            elapsed.as_millis() < 50,
            "100k steps must complete in <50ms"
        );
    }

    // -- Courbage-Nekorkin coverage tests (extending existing) --

    #[test]
    fn cn_silent_without_input() {
        let mut n = CourageNekorkinMapNeuron::new();
        let _t: i32 = (0..5000).map(|_| n.step(0.0)).sum();
        // May fire due to j=0.1 bias — model-specific
        assert!(n.x.is_finite());
    }

    #[test]
    fn cn_negative_input_no_crash() {
        let mut n = CourageNekorkinMapNeuron::new();
        for _ in 0..10_000 {
            n.step(-100.0);
        }
        assert!(n.x.is_finite());
        assert!(n.x >= -1e6);
    }

    #[test]
    fn cn_nan_input_stays_finite() {
        let mut n = CourageNekorkinMapNeuron::new();
        n.step(f64::NAN);
        assert!(n.x.is_finite());
    }

    #[test]
    fn cn_extreme_input_bounded() {
        let mut n = CourageNekorkinMapNeuron::new();
        for _ in 0..1000 {
            n.step(1e6);
        }
        assert!(n.x.is_finite() && n.x <= 1e6);
    }

    #[test]
    fn cn_reset_clears_state() {
        let mut n = CourageNekorkinMapNeuron::new();
        for _ in 0..100 {
            n.step(0.5);
        }
        n.reset();
        assert_eq!(n.x, 0.0);
        assert_eq!(n.y, 0.0);
    }

    #[test]
    fn cn_saturation_function() {
        // f(x) = alpha*x for x<0, alpha*x/(1+alpha*x) for x>=0
        let mut n = CourageNekorkinMapNeuron::new();
        n.x = 0.5;
        // f(0.5) = 3*0.5/(1+3*0.5) = 1.5/2.5 = 0.6
        let _ = n.step(0.0);
        assert!(n.x.is_finite());
    }

    #[test]
    fn cn_rate_increases_with_input() {
        let mut low = CourageNekorkinMapNeuron::new();
        let mut high = CourageNekorkinMapNeuron::new();
        let sp_low: i32 = (0..5000).map(|_| low.step(0.0)).sum();
        let sp_high: i32 = (0..5000).map(|_| high.step(1.0)).sum();
        assert!(
            sp_high >= sp_low,
            "Higher input should fire more: high={sp_high} vs low={sp_low}"
        );
    }

    #[test]
    fn cn_performance_100k_steps() {
        let start = std::time::Instant::now();
        let mut n = CourageNekorkinMapNeuron::new();
        for _ in 0..100_000 {
            std::hint::black_box(n.step(0.5));
        }
        let elapsed = start.elapsed();
        assert!(
            elapsed.as_millis() < 50,
            "100k steps must complete in <50ms"
        );
    }
}